The present invention relates to a polycarbonate resin composition, and more particularly it relates to a polycarbonate resin composition having an excellent resistance to an ionizing radiation, in which a compound containing oxymethylene unit, a compound containing oxymethylene unit having substituent or a cyclic ether compound having substituent is blended therewith.
Polycarbonate resins have been widely utilized in the fields of medical supplies and appliances because the polycarbonate resins have excellent mechanical strength, impact resistance, heat resistance and transparency as well as a high safety.
The medical supplies and appliances are generally sterilized upon use. Specifically, the sterilization of these medical supplies and appliances has been carried out by a high-pressure steam sterilization process, an ethyleneoxide gas (EOG) sterilization process, or a sterilization process using an ionizing radiation such as a gamma radiation or an electron beam. Among these sterilization processes, the high-pressure steam sterilization process has disadvantages such as high energy cost and necessity of a drying step after the sterilization. Similarly, the EOG sterilization process has caused such problems as toxicity of ethyleneoxide itself or environmental pollution upon disposal thereof. Under these circumstances, a recent tendency is such that the sterilization process using an ionizing radiation, generally a gamma radiation has been predominately adopted because the sterilization process is relatively inexpensive and can be performed at a low temperature in a dry condition.
However, there also is such a problem that the polycarbonate resin suffers from yellow discoloration when exposed to the ionizing radiation for sterilization thereof. This results in considerable deterioration in utility value of the products, especially when the polycarbonate resin is applied to the medical supplies or appliances.
As means for solving these problems, there have been proposed a polycarbonate resin composition in which a halogen-containing polycarbonate resin is blended (Japanese Patent Application Laid-open (KOKAI) No. 2-55062 (1990)), a polycarbonate resin composition in which a brominated phthalic acid derivative is blended (Japanese Patent Application Laid-open (KOKAI) No. 5-179127 (1993)), or the like. However, metal corrosion is likely to generate due to the halogen in the resin compositions, so that a molding machine or the like therefor are required to be made from special metal material having a corrosion resistance.
In order to solve the afore-mentioned problems such as yellow discoloration or the like, there have been also proposed a polycarbonate resin composition in which thio-alcohols are blended (Japanese Patent Application Laid-open (KOKAI) No. 1-229052 (1989)), a polycarbonate resin composition in which thio-ethers are blended (Japanese Patent Application Laid-open (KOKAI) No. 2-115260 (1990)), a polycarbonate resin composition in which compounds having a mercapto group are blended (Japanese Patent Application Laid-open (KOKAI) Nos. 2-49058 (1990), 4-36343 (1992) and 6-166807 (1994)), a polycarbonate resin composition in which polyalkylene-oxide and an aromatic compound having a sulfonate group are blended in combination (Japanese Patent Application Laid-open (KOKAI) No. 5-209120 (1993)), and a polycarbonate resin composition in which compounds having a sulfide group are blended (Japanese Patent Application Laid-open (KOKAI) No. 6-93192 (1994) and 6-248170 (1994)). However, there still exist such problems that the yellow discoloration cannot be sufficiently prevented, or environmental conditions deteriorate due to generation of malodor upon forming, or the like.
Furthermore, in order to solve the afore-mentioned problems, Japanese Patent Application Laid-open publication (KOKAI) No. 61-215651 (1986) discloses a polycarbonate resin composition in which boron compounds are blended, Japanese Patent Application Laid-open (KOKAI) No. 62-135556 (1987) discloses a polycarbonate resin composition in which polyetherpolyol or an alkyl ether thereof are blended, Japanese Patent Application Laid-open (KOKAI) No 2-232258 (1990) discloses a polycarbonate resin composition in which benzyl alcohol derivatives are blended, and Japanese Patent Application Laid-open (KOKAI) No. 2-132147 (1990) discloses a polycarbonate resin composition in which itaconic acid, benzaldehyde-dimethylacetal, benzaldehyde-propyleneglycolacetal, etc. are blended. However, there have caused such problems that the yellow discoloration cannot be sufficiently prevented or otherwise, if the amounts of the compounds used therein increases to an extent sufficient to prevent the yellow discoloration, the other properties of the polycarbonate resin compositions are adversely affected.
In view of these problems encountered in the prior arts, it is demanded in a polycarbonate resin composition to maintain the inherent properties thereof, generate little malodor upon forming and prevent generation of yellow discoloration upon irradiation of an ionizing radiation for sterilization.
As a result of the present inventors' earnest studies for solving the afore-mentioned problems, it has been found that a polycarbonate resin composition prepared by blending a compound containing oxymethylene unit, a compound containing oxymethylene unit having substituent or a cyclic ether compound having substituent and a specific compound with a polycarbonate resin at specified blending ratios, not only maintains inherent properties of polycarbonate resin without deterioration but also prevents generation of yellow discoloration upon sterilization using an ionizing radiation. The present invention has been achieved on the basis of the findings.